Membranes enjoy widespread use. One frequent application is in machines having a hydraulic or pneumatic drive. In such machines, movement of the membrane transports a fluid. Membrane or diaphragm pumps are also widely used in the pharmaceutical, biological, and foodstuff industries. In such applications, a high degree of purity of the transported fluid is important. Another application field is the chemical industry, in which it is of primary importance that the transported fluid not leak out, since it may be poisonous, toxic, or flammable. In such applications, it is desirable, and sometimes necessary, that the membrane be constantly checked for integrity. Several mechanisms are known which perform this function.
The published German Patent Application No. DE OS 37 29 726 describes a membrane-machine unit that having at least two membranes which form a gap between them that is connected to a fluid leak sensor. If one or the other membrane is ruptured, the fluid enters the gap between the membranes, and the sensor reports the leak. Such a device is relatively inefficient in design, and problems may only be detected after a relatively large amount of fluid has leaked. Also, the effect may only be measurable after the closely-positioned membranes are forced apart by the leaking fluid.
Only then can the fluid reach the sensor. Additionally, the fluid must also reach the sensor""s location.
The published European Patent No. EP 0 486 618 describes another arrangement for detecting a membrane fault wherein two membranes are mounted with a sensor between them to detect the presence of fluid between the membranes. Here also, the detection occurs only after a large quantity of fluid has entered the space between the two membranes. Additionally, the design of the membranes with the accompanying detector is very inefficient.
The European Patent No. EP 0 715 690 presents yet another method of detecting a damaged membrane. This patent provides a pump membrane that contains a layer of sealed, porous polytetrafluorethylene (PTFE) in which an electrically-conducting fiber made of expanded porous PTFE is embedded. The ends of the fiber are connected to an electrical measuring device. By measuring changes in conductivity of the fiber, fatigue or cracks in the membrane may be detected. This design has the disadvantage that it is very expensive to produce, and is therefore associated with high cost.
The principal object of the present invention is to provide a device to detect leaks or fatigue in membranes that is simple in design and may be produced at low cost.
This object, as well as other objects which will become apparent from the discussion that follows, are achieved, in accordance with the present invention, by constructing the membrane of two membrane layers to form a double membrane, and providing at least one of the membrane layers with at least one conductor that results in a change in measured value in response to any change in either the membrane or the conductor.
With such a membrane construction, optical devices used to detect fluid accumulations are no longer required, and it is also no longer necessary to embed an electrical conductor directly into a membrane layer. Along with an advantageous simplicity of manufacture, there is also the advantage that damage to the membrane, as well as the magnitude of the damage, may be detected quickly.
A very simple option exists of emplacing electrically-conducting metal conductors or elastomer loops. Loops may, for example, be arranged radially in the membrane. Other configurations are certainly possible.
Based on another implementation of the invention, an optical fiber consisting of a glass or plastic fiber might be added to a membrane layer. Such an optical conductor could be in the form of a closed spiral circuit or open conductor spiral with reflecting end.
The conductor might also consist of a channel mounted on a membrane layer that contains a fluid. The channel would be arranged concentrically around the membrane layer center.
In a particularly space-saving and easy-to-produce monitoring device according to the invention, the conductor comprises a conductive xe2x80x9cfleecexe2x80x9d material (a fabric of non-woven material) or piece of elastomer. Thus, the entire surface of the pertinent membrane layer may be coated so that a very precise location of a fault could be determined. The fleece piece might be produced from a fleece containing carbon fiber. This would allow various configurations to be pressed out. Formation of the piece of fleece or elastomer as a fabric made of metallic or carbon fibers is a further possibility.
Another very useful implementation of the invention might include an elastomeric element containing metal or carbon particles that are imprinted onto the membrane layers using a silkscreen method. This would produce a particularly flat membrane.
Another advantageous implementation might be achieved by using an elastomer conductor formed from an electrically-conducting foil vulcanized onto the membrane layer.
This new membrane monitoring device would in principle be formed of two membrane layers, where at least one would contain a conductor on its inner surface that detects damage to the membrane and passes a signal to a measurement or signaling device attached to it. This results in a layered construction of the membrane consisting of membrane layer, conductor layer, and membrane layer in its simplest form. The membrane layers could be produced from materials suitable to the membrane application. One very useful implementation form, particularly when the membrane is used for foodstuffs or chemical products, would be achieved if the membrane layer in contact with the fluid being transported were made of PTFE (polytetrafluorethylene) and the exterior membrane layer were made of an elastomer. The PTFE membrane layer would be particularly resistant to aggressive chemical substances, while the elastomer membrane layer would be very flexible. If a leak occurred in the PTFE membrane layer, it would be detected via the monitoring conductor mounted on the inner side of that membrane layer and reported. The elastomer membrane layer would itself remain intact, fulfilling the function of a second barrier. The most advantageous form of the membrane would be achieved if the membrane were to consist of a double membrane made using a PTFE (or similar material) membrane layer and an elastomer membrane layer, wherein each membrane layer be coated on its inner surface with a layer of electrically-conducting material, and wherein the layers be separated from each other by an electrically-insulating porous fleece layer. Production of such a membrane is relatively simple, and the entire surface of the membrane would be coated so that even the most minor damage could be detected.
Mounting of the conductors onto each membrane layer could be achieved using various methods. Advantageous options include thermal adhesive, vulcanization, or similar methods.
For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.